(I) Field of the Invention
The present invention relates to a beam scanning device, such as a cathode-ray tube used in a color image display device such as a terminal display of a color television receiver or a computer.
(II) Description of the Prior Art
Conventionally, many flat cathode-ray tubes (CRT) for television receivers have been available. Typical examples (SID 176 Digest) of the flat cathode-ray tubes which are developed by Zenith Corp. and State University of Arizona are illustrated in FIGS. 1 and 2. In the CRT shown in FIG. 1, horizontal stripe cathodes 11 are vertically aligned parallel to each other. Electron beams emitted from the cathodes 11 are incident on an electron multiplier section 12 to multiply the electrons. The electron beam produced from the electron multiplier section 12 is horizontally expanded in a sheet-like manner. This electron beam is modulated with a color signal by modulation electrodes 14 so as to control the amount of the electron beam passing through the modulation electrodes 14. The controlled electron beam is accelerated by a high anode voltage applied to a phosphor screen 16, thereby activating the phosphors. Electrodes 13 and 15 are used to focus the electron beams. The modulation electrodes 14 are vertically aligned to be parallel to each other and are spaced apart from each other. Different color signals are applied to the respective modulation electrodes 14, respectively, so that a horizontal color image is displayed by horizontal scanning or main scanning on the phosphor screen 16. The subscanning is vertically performed by controlling the cathode potential, so that a two-dimensional color image is displayed on the screen 16.
In the CRT shown in FIG. 2, the cathodes 11 and the electron multiplier section 12 shown in FIG. 1 are modified. Stripe cathodes 22 are arranged between a back plate 21 and mesh electrodes 23 and 24 so as to set an incident angle of the electron beam to be normal to the electrode 13. Any other component of the CRT shown in FIG. 2 is the same as that shown in FIG. 1. The same reference numerals used in FIG. 1 denote the same parts in FIG. 2, and a detailed description thereof will be omitted.
The design of the modulation electrodes 14 presents a problem in the conventional flat CRTs shown in FIGS. 1 and 2. In order to perform color display, R (red), G (green) and B (blue) phosphor stripes 31 are generally formed to constitute a phosphor screen, as shown in FIG. 3. Modulation electrodes 32 must be aligned with the phosphor stripes, respectively. In this case, each set of R, G and B phosphor stripes constitutes a pel or picture element. In order to obtain a high-resolution image, the width of the phosphor stripes must be greatly decreased. Assume that a screen size of 10 inches is given. In order to obtain 340 horizontal pels in this 10" screen, a width of one pel along the horizontal direction becomes about 600 .mu.m. When this pel is displayed by the R, G and B components, a width of each phosphor stripe becomes 200 .mu.m. Therefore, the modulation electrodes 32 must be provided at a pitch of 200 .mu.m. It is difficult to arrange the modulation electrodes 32 at this pitch. Furthermore, about 1,000 modulation electrodes must be used, thus resulting in complex electrical connections.